New results on XYZ states from e + e - experiments Changzheng Yuan ( 苑 长 征 ) IHEP, Beijing (BESIII, Belle, Belle II) The 6th International Workshop on Charm Physics 31 Aug - 4 Sept 2013; Manchester, England 1

2 Outline Introduction New information on the X(3872) Update the ISR Y-family analyses and more … Z c (3900), Z c (4020) & Z c (4025) Summary & Outlook new Absolutely new

3 Results are from these experiments BESIII CLEOc

4 The Beijing Electron Positron Collider My office LINAC BEPCII (Beijing electron- positron collider) BESIII detector Main entrance to IHEP Satellite view of IHEP, Beijing Founded: 1984, Ecm=2-5 GeV (BEPC): L peak =1.0x10 31 /cm 2 s 2008-now (BEPCII): L peak =7x10 32 /cm 2 s

5 BESIII: production of charmonium(like) states Vector  /Y states can be produced directly C-even states can be produced from radiative transitions From PDG BEPCII can reach here!

BESIII collected 3.3/fb for XYZ study

7 Charmonium spectroscopy n (2S+1) L J n radial quantum number S total spin of c & cbar L orbital angular momentum L = 0, 1, 2... correspond to S, P, D, … J = S + L P = (–1) L+1 parity C = (–1) L+S charge conj. Godfrey & Isgur, PRD32, 189 (1985) States below charm threshold are all observed now, still many missing states above charm threshold. Talk by J. Z. Zhang this afternoon !

8 There are lots of XYZ states X(3872) XYZ(3940) X(3915) X(4160) Y(4008) Y(4140) Y(4260) Y(4360) X(4350) Y(4660) X(3915) X(4160) Y(4008) Y(4140) Y(4260) Y(4360) X(4350) Y(4660) Z(4430) Z(4250) Z(4050) Z(3900) Z(4020) Z(4025) What are they ? Charmonium? Hybrid? Tetraquark? Molecule? … Not all of them are charmonia! ? Charmonium in the final state, but not an obvious charmonium state ( charmoniumlike or XYZ )。

9 What is the X(3872)? Mass: Very close to  D 0 D *0 threshold Width: Very narrow, < 1.2 MeV J PC =1 ++ [ LHCb ] Production –in  pp/pp collison – rate similar to charmonia –In B decays – KX similar to  cc, K*X smaller than  cc –Y(4260)   +X(3872) [BESIII, see next slides] Decay BR: open charm ~ 50%, charmonium~O(%) Nature (very likely exotic) –Loosely  D 0 D *0 bound state (like deuteron?)? –Mixture of excited  c1 and  D 0 D *0 bound state? –Many other possibilities (if it is not  ’ c1, where is  ’ c1 ?) M(  J/  ) –M(J/  ) [GeV] Belle, /fb

10 Observation of e + e -   X(3872)   +  - J/  Clear ISR  ’ signal for data validation X(3872) signal at around GeV BESIII preliminary Ecm=4.01 GeVEcm=4.23 GeV Ecm=4.26 GeVEcm=4.36 GeV

Observation of e + e -   X(3872) ISR  ’ signal is used for rate, mass, and mass resolution calibration. N(  ’)=1242 ; Mass=  0.05 MeV;  M =1.84  0.06 MeV N(X(3872))=15.0   M(X(3872)) =  0.8  0.3 MeV [PDG:  0.17 MeV] BESIII preliminary 11

Observation of e + e -   X(3872) BESIII preliminary 12

Y-family states (vectors observed in Initial State Radiation) + e + e -   +  - h c from BESIII 13

14 The Y states PRL99, /fb PRL99, /fb PRL95, /fb PRL98, /fb PRL101, /fb M(  c +  c - ) Above  DD threshold, decay to open charm? Y(4008) Y(4260) Y(4360) Y(4660) Y(4630)

15 The Y states Belle: PRL99, , 673/fb PRL110, /fb PRD86, /fb BaBar: , 520/fb Y(4008): confirmed by Belle with more data; events observed at BaBar, fit with exponential Wait for BESIII Y(4660): confirmed by BaBar Y(4630): no data, a bit beyond BEPCII/BESIII limit

16 Update ISR  +  - J/  analysis Lum=967fb -1 Event selections are almost the same as in previous Belle published paper PRL99, (2007) ▼ Clean  (2S) signal events are obtained, purity>99%. ▼ Fit with double Gaussian yields M(  (2S)) = (3686.1±0.2) MeV,  =4.8MeV ▼ ISR Ψ(2S) production cross sections agree with calculations Belle also observed a few  (3770)      J/  events  N=54±20, 2.8  B(  (3770)      J/  )=(5.5±2.1)×10 -3, PDG (1.93±0.28 ×10 -3 ) 16

Two-resonance fit 1.Fit with two coherent resonances |BW 1 +BW 2 *exp(i  )| 2 +bkg. 2.Mass of Y(4008) is lower than before 3.Fit quality:  2 /ndf=101/84, confidence level is 9.3% R 1 =Y(4008) R 2 =Y(4260) Still observed two resonances, Y(4008) and Y(4260), agrees with Belle’s previous results. 17

18 Select e + e -   +  - J/  at 4.26 GeV Select 4 charged tracks and reconstruct J/  with lepton pair. Very clean sample, very high efficiency (~45%).  (e + e -   +  - J/  )= (62.9  1.9  3.7) pb BESIII: PRL110,  33 J/    +   28 J/   e + e -

19 Cross section of e + e -   +  - J/  Belle: PRL110, BaBar: PRD86, (2012) BESIII:  (e + e -   +  - J/  ) = (62.9  1.9  3.7) pb Agree with BaBar & Belle! Best precision! BESIII: PRL110, BESIII is measuring cross sections at more energy points, and will take more data!

20 e + e -   +  - h c (1P) at BESIII h c  c,  c  hadrons [16 exclusive decay modes]  p  p,  +  - K + K -,  +  - p  p, 2(K + K - ), 2(  +  - ), 3(  +  - )  2(  +  - )K + K -, K S 0 K +  - +c.c., K S 0 K +  -  +  - +c.c., K + K -  0  p  p  0, K + K - ,  +  - ,  +  -  0  0, 2(  +  - ) , 2(  +  -  0 ) Ecm=4.26 GeVEcm=4.36 GeV BESIII preliminary

Observation of e + e -   +  - h c (1P)  (h c )=416  28 Lum=827/pb   = 41.0  2.8  7.4 pb  (h c )=357  25 Lum=544/pb   = 52.3  3.7  9.2 pb Ecm=4.26 GeV BESIII preliminary 21 Ecm=4.36 GeV

Observation of e + e -   +  - h c (1P)  (e + e -   +  - h c ) ~  (e + e -   +  - J/  ) but line shape different Local maximum ~ 4.23 GeV Hint for a vector  ccg hybrid? [ PRD78, (Guo); (Dudek):  cc in spin-singlet in hybrids!] 22 BESIII preliminary

Comparison of e + e -   +  - h c and  +  - J/  Broad structure at ~4.4 GeV? Need more data at high energies to complete the line shape measurement. Open circles: Belle e + e -   +  - J/  Solid dots: BESIII e + e -   +  - h c 23

24 What are the Y states? Between 4 and 4.7 GeV, at most 5 states expected (3S, 2D, 4S, 3D, 5S), 7 observed Hybrids are expected in this mass region Molecular states? Cannot rule out threshold effect/FSI/… Y(4260), Y(4360), Y(4660) are all narrow and similar  +  - h c add complexity

25 Z c : charged charmoniumlike states Find a clear signature for exotic state! Decays to charmonium thus has a  cc pair! With electric charge thus has two more light quarks!  N quark  4 ! Do searches in π  J/ψ, π  h c (1P), π  ψ(2S), π   cJ, … BESIII: e + e -  π  +exotics,   +exotics, …

e + e -   +  - J/  at Ecm=4.26 GeV 26 BESIII: PRL110, evts in J/  signal region, purity~90%

27 e + e -   +  - J/  from ISR Belle: PRL110, M 2 (  ) vs. M 2 (  J/  ) for 4.15<M(  J/  ) <4.45 GeV 2.(inset) Background events in J/  -mass sidebands 3.Structures both in  and  J/  systems evts in J/  signal region, purity~80%

Z c (3900) observed in two experiments! 28 BES3 at 4.26 GeV: Belle with ISR: M =  6.6  4.5 MeV  = 63  24  26 MeV 159  49 events >5.2  M =  3.6  4.9 MeV  = 46  10  20 MeV 307  48 events >8   Talk by Zhiqing Liu on Monday

29 CLEOc data at 4.17 GeV: M = 3885  5  1 MeV  = 34  12  4 MeV 81  20 events 6.1  Confirmed with CLEOc data! BESIII Belle

30 Couples tocc Has electric charge At least 4-quarks What is its nature? DD * molecule? Tetraquark state? Cusp? Threshold effect? … Predictions and more experimental information will be essential to understand its nature.  A partner below/above Z c ? What is Z c (3900)?  Panel discussions on Monday

Dalitz plot of e + e -   +  - h c (1P) BESIII preliminary 31

e + e -   Z c (4020)   +  - h c (1P) Ecm=4.26 GeVEcm=4.36 GeV Simultaneous fit to 4.26/4.36 GeV data and 16  c decay modes. 6.4  M(Z c (4020)) =  1.0  2.5 MeV;  (Z c (4020)) = 5.7  3.4  1.1 MeV N= 64  19 N= 56  17 BESIII preliminary 32

33 e + e -   - (D*D*) + +c.c. at BESIII 827 pb -1 data at Ecm=4.26 GeV Tag a D + and a bachelor  -, reconstruct one  0 to suppress the background. BESIII: , submitted to PRL

34 e + e -   - (D*D*) + +c.c. at BESIII BESIII Remove DD, DD*, D*D*, DsDs, … removed

e + e -   Z c (4025)   - (D*D*) + +c.c. Fit to   recoil mass yields 401  47 Z c (4025) events. > 10  M(Z c (4025)) =  2.6  3.7 MeV;  (Z c (4025)) = 24.8  5.6  7.7 MeV BESIII:

36 Z c (4020)=Z c (4025)? M(4020) =  1.0  2.5 MeV M(4025) =  2.6  3.7 MeV  (4020) = 5.7  3.4  1.1 MeV  (4025) = 24.8  5.6  7.7 MeV Close to D*D* threshold=4017 MeV Mass consistent with each other but width ~2  difference Interference with other amplitudes may change the results Coupling to  D*D* is much larger than to  h c if they are the same state Will fit with Flatte formula

What next at BESIII? Precise resonant parameters Spin-parity of Z c and Z c ’ More decay modes [  ’,  c, open charm,…] Production mechanisms, production rates Test various theoretical models Neutral partners of Z c and Z c ’ Excited Z c, Z c ’ states? Z cs  KJ/  states? Other XYZ states? More data at high energies 37

38 Summary Lots of progress in XYZ studies in e + e - experiments BESIII started study of the XYZ particles Observation of Y(4260)   X(3872) New information on the Y’s from BaBar and Belle. Y(4660) confirmed, Y(4008) not confirmed; large  +  - h c production rate above 4.2 GeV First confirmed exotic state with at least four quarks, Z c (3900) +, at BESIII & Belle Observation of the Z c ’ at BESIII More results will come soon, stay tuned! Thanks a lot!

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40 Belle observed Z(4430) ± →ψ(2S)π ±  Found in ψ(2S)π + from B→ψ(2S)π + K. Z parameters from fit to M(ψ(2S)π + )  Confirmed through Dalitz-plot analysis of B→ψ(2S)π + K  B→ψ(2S)π + K amplitude: coherent sum of Breit-Wigner contributions  Models: all known K*→Kπ + resonances only all known K*→Kπ + and Z + →ψ(2S)π +  favored by data  [cu][cd] tetraquark? neutral partner in ψ’π 0 expected  D*D 1 (2420) molecule? should decay to D*D*π PRL100, (2008) PRD80, (2009) Significance: 6.4σ Significance: 6.4σ M 2 (ψ(2S)π + ) M 2 (Kπ + ) K*(890) K 2 *(1430) Z + (4430) M 2 (ψ(2S)π + ) after K* veto 657M BB – ̶̶̶̶̶̶ – ̶̶̶̶̶̶ fit for model with K*’s only – ̶̶̶̶̶̶ – ̶̶̶̶̶̶ fit for model with K*’s and Z

41 Spin-parity of the Z(4430) ±  B→ψ(2S)π + K amplitude: coherent sum of Breit-Wigner contributions arXiv: Significance: 6.4σ Significance: 6.4σ

42 BaBar doesn’t see a significant Z(4430) + “For the fit … equivalent to the Belle analysis…we obtain mass & width values that are consistent with theirs,… but only ~1.9  from zero; fixing mass and width increases this to only ~3.1 .” Belle PRL: (4.1 ± 1.0 ± 1.4)x10 -5 PRD79, (2009)

43 Belle observed Two Z ± →χ c1 π ±  Dalitz-plot analysis of B 0 →χ c1 π + K - χ c1 →J/ψγ with 657M BB  Dalitz plot models: known K*→Kπ only K*’s + one Z →χ c1 π ± K*’s + two Z ± states  favored by data M(χ c1 π + ) for 1<M 2 (K - π + )<1.75GeV 2 –̶̶̶̶̶̶ –̶̶̶̶̶̶ fit for model with K*’s –̶̶̶̶̶̶ –̶̶̶̶̶̶ fit for double Z model –̶̶̶̶̶̶ –̶̶̶̶̶̶ Z 1 contribution –̶̶̶̶̶̶ –̶̶̶̶̶̶ Z 2 contribution PRD 78, (2008) Significance: 5.7  Significance: 5.7 

44 BaBar doesn’t see significant Z ± →χ c1 π ± “We find that it is possible to obtain a good description of our data without the need for additional resonances in the  c1  system.” PRD85, (2012) Belle: ( )x10 -5 Belle: ( )x10 -5

M(  J/  )  [4.2, 4.4] GeV via ISR 548/fb at GeV Peaks at 12 & 15 GeV 2 ? Shown at QWG’

Observation of the X(3823) arXiv: (submitted to PRL) M χc1γ (GeV/c 2 ) B  χ c1 γK The measured mass and width are consistent with the missing Ψ 2 (1D) state BESIII may search for it! 711 fb σ 46

47 BEPC II: BEPC II: Large crossing angle, double-ring RF IP Beam energy: GeV Luminosity: 1×10 33 cm -2 s -1 Optimum energy: 1.89 GeV Energy spread: 5.16 ×10 -4 No. of bunches: 93 Bunch length: 1.5 cm Total current: 0.91 A SR mode: 2.5 GeV Compton back-scattering for high precision beam energy measurement BESIII is here

48 BESIII Detector Be beam pipe SC magnet, 1T Magnet yoke MDC, 130  m 0.5% at 1 GeV/c CsI(Tl) calorimeter, 1 GeV TOF, 90ps RPC Total weight 730 ton, ~40,000 readout chnls, Data rate: 5kHz, 50Mb/s

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